The present invention relates to an optimizing control method and an optimizing control system for efficiently controlling a power plant which supplies energy such as electricity and steam to a factory or the like. The present invention particularly provides effective means for optimizing the load distribution between a plurality of boilers or turbines operated in parallel in a power plant.
The present invention also provides an optimum operation control method and an optimum operation control system for efficient control of the abovementioned power plant in view of scheduling factors such as seasonal fluctuations in the demands for electricity and steam, a unit electricity price and a unit fuel price, and at the minimum cost for a prescribed period.
FIG. 9 shows an example of a power plant employed for example in a petrochemical factory. The plant includes boilers 1, 2 using heavy oil or fuel gas as a fuel, turbines 3, 4 to generate steam and electricity, a condensing turbine 5 dedicated to power generation, generators 6, 7, 8 to convert energy into electricity, a boiler main steam base pipe 20, a steam base pipe 21 to supply steam and electricity to a factory 23, and an electric bus 22.
PID control devices are provided in a part of the power plant. More specifically, there are provided a PID control device 13 to control the boiler main steam pressure, a PID control device 14 to control the fuel flow rate of the boiler 2, a PID control device 15 to control the steam pressure, a PID control device 16 to control the steam flow rate of the turbine 4, and a PID control device 17 to control the amount of power generated by the generator 8, so that supply of energy is balanced with the demand. It is to be noted that only some of the PID control devices for boilers and turbines are shown for ease of illustration.
The load distribution among the boilers is achieved by the operator manually adjusting the value set at the PID control device 14 which controls the fuel flow rate, while the load distribution among turbines is achieved by manually adjusting the value set at the PID control device 16 which controls the steam flow rate. The amount of electricity to receive from an electric power company is controlled by manually adjusting the value set at the PID control device 17 which controls the amount of energy generation.
At the time of such manual adjustment, there has been an attempt to provide the operator with an optimum operation guideline in view of the economical efficiency of the plant as a whole (see for example xe2x80x9cSteam Balance Optimization in Chemical Plant.,xe2x80x9d Proceedings of IFAC Symposium ADCHEM ""94 (1994)). In this attempt, the optimum calculation is executed based on a linear model of the plant, and the operation adjustment based on the result is left in the hands of the operator.
It is known that the scheduling problem to obtain a yearly or monthly optimum operation pattern for a power plant is solved by a heuristic method or mathematical programming. However, the result can hardly be reflected on-line upon an actual plant, and the operation adjustment is again put in the hands of the operator.
Meanwhile, the following three problems are encountered in the above control system.
Firstly, it is much mentally distressing for the operator to consider the economical efficiency of a power plant as a whole and frequently adjust the boilers and turbines according to constantly changing supply and demand of steam and electricity to make sure that the boilers and turbines operate in an optimum state. This is quite difficult and the operation necessarily fails to satisfy the optimum operation condition.
Secondly, the model to evaluate the economical efficiency of a power plant as a whole is a linear model based on past record data, and therefore does not take into account the non-linearity of the plant. The model could therefore depart from the real optimum operation condition when the operation condition changes.
Thirdly, the boilers 1,2 and the turbines 3, 4, 5 are closely related with each other through the boiler main steam base pipe 20, and the steam base pipe 21, and the generators 6, 7 and 8 depend on the turbines 3, 4 and 5, respectively. The amount of electricity to receive and the amount of electricity to generate are related through the electric bus. Therefore, the control systems in the power plant interfere with each other and fluctuations in the supply and demand balance of electricity and steam in the plant as a whole can hardly be absorbed in a short period of time.